This invention relates to a backflow preventer.
Backflow preventers are principally used to prevent contamination of a public water distribution system by reducing or eliminating backflow or back-siphonage of contaminated water into the system. Usually, the backflow prevention assembly is installed in a pipeline between a main supply line and a service line that feeds an installation, e.g., a hotel factory or other institution, or even a multiple or single family residence. A backflow prevention assembly typically includes two check valves that are configured to permit fluid flow only in the direction from the main supply line to the service line.
FIG. 1 illustrates a conventional connection between a valve module 40xe2x80x2 and a housing 20xe2x80x2 of a prior art backflow preventer. As shown, an annular mount 90 having an threaded inner surface 92 and a smooth outer surface 94 is secured to a cylindrical inner surface 96 of housing 20xe2x80x2, e.g., by solder 98 or welding 99. The valve module 40xe2x80x2 is then screwed into mount 90 to secure it to the housing.
In one aspect the invention is directed to a backflow prevention assembly. The backflow prevention assembly has a unitary housing with a passage therethrough, two threaded regions formed in an inner surface of the unitary housing, and two valve assemblies positioned in the passage to prevent fluid flow in a direction. Each valve assembly has an annular mount having a threaded outer surface that engages one of the threaded regions on the inner surface of the housing.
Implementations of the invention may include the following features. The two valve assemblies may be cam-check valves. The threaded regions may be formed by a thread rolling process, e.g., by placing a threaded die against the inner surface of the housing and pressing on an outer surface of the housing. Threaded regions may also be formed in the outer surface of the unitary housing.
In another aspect the invention is directed to a method of forming threads in a tubular housing. In the method, a die having a thread on an outer surface thereof is placed in contact with an inner surface of a unitary housing having a passage therethrough. The outside of the housing is pressed to drive the inner surface against the threads on the outer surface of the die to form threads on the inner surface of the housing.
Implementations of the invention may include the following features. The thread on the outer surface of the first die may be generally the inverted shape of the threads to be formed on the inner surface of the housing. A second die having a thread formed on an outer surface thereon may be used to press on the outside of the housing. Two valve assemblies may be positioned in the passage to prevent fluid flow in a direction, each valve assembly having an annular mount having a threaded outer surface that engages one of the threaded regions on the inner surface of the housing. A port may be formed in a wall of the housing.
Advantages of the invention may include the following. The backflow prevention assembly is easier to assemble, e.g., in the field, and is less expensive to manufacture than currently available backflow prevention assemblies for similar applications.
Other features and advantages of the invention will become apparent from the following detailed description including the drawings and the claims.